Process of manufacturing sulphite pulp



Patented Aug. 28, 1934 No SULPHITE Ernstf Hocl1berger Hawks-shu s, criteria, (a... ada'yassignorto'Canadian International Paper i Gompany,-"Montreal,'QuebecQCanada 7N6 Drawing. App ication June 3', i933, gas-1 No. 674,222. In Canada June .z d lggg 8 Claims. (Cl, 92L 11 :l'

This invention relates to the manufacture of sulphite pulp and particularly to a two-stage cooking process resulting in substantial economies of operation and in the production of a 15? high quality pulp.

In co-pending applications Serial No. 674,223 and Serial No. 674,224, processes of this character are disclosed. The present invention relates to a further improvement in these processes.

10? Economy in operation in the manufacture of pulp is an important consideration but in addition it is an object of this invention to provide a process whereby full advantage may be taken of the hydrogen ion concentration developed during the ifinal stage of the cooking operation.

In carrying out the invention a two-stage cooking process is employed. In the first stage the cellulose material is cooked with a liquor capable of supplying the bisulphite ions required to effect 'Isulphonation of the lignin. This liquor may be an aqueous solution of calcium and/or magnesium bisulphite, containing an excess of free sulphurous acid, alkali sulphite or bisulphite with or without free sulphurous acid, or a mixture of 25. these constituents. In this cooking operation liberation of the fibre is substantially avoided and reaction products, harmful in later stages of the process, are removed. At the conclusion of this step the liquor is removed without substantially 3llj'jlowering'the temperature and pressure in the digester, preferably by the introduction of direct steam into the top portion of the digester; In some cases, it is preferable to wash the charge with hot water, a preheated sulphurous acid soflo'zilution or with a portion of preheated liquor, such s is used in the cooking operation. This insures complete removal of undesired products and leaves the charge in best condition for the final fibre-liberating cook.

The second stage requires the cooking of the charge with water, preheated to the temperature of the charge in the digester. The temperature and pressure in the digester are then raised above the limits employed in the usual one-stage sulphite process and these conditions are maintained until fibre liberation is complete and the remaining encrusting materials about the cellulose fibre are dissolved. Under these conditions it is found that the hydrolysis of the sulphonated lignin is Bo -(effected without damage to the cellulose fibre and without the use of added expensive reagents. This is probably due to the release of hydrogen ions from reaction products, such as organic acids, formed during the cooking operation.

555; To further illustrate the method of carrying out theinvention the following specific examples may be given.

(1) Chips of coniferous wood or the like are treated in a digester with a liquor consisting of an aqueous solution of calcium and magnesium tially constant, and preheated water is added.

The temperature is then raised to 160 to 170 C. with a pressure of to 100 pounds and maintained for 3 to 9 hours,'until fibre liberation, is complete. The contents of the digester are then dumped in the usual way.

(2) The chips may be cooked with a first-stage liquor consisting of a solution of substantially pure sodium bisulphite, having a combined S02 content in the proportion of substantially 50% of the total S02 and containing, for example, 6 to 80.

8% total S02 and 3 to 4% combined S02. Cooking is continued for 3 to 11 hours until a temperature of 100 to 150 C. is reached. The duration of the cook after this temperature is reached may vary from 1 to 8 hours. This liquor is then re- 85 moved as before and the second-stage treatment is effected with preheated water. The temperature is raised to 160 to 170 C. with a pressure of 85 to 100 pounds. Fibre liberation is completed within 10 to 14 hours from the start and the digester contents are dumped and washed as required.

It will be apparent that the invention provides for substantial economy in the use of chemical reagents employed, these reagents being used only in the first stage cooking operation for removal of fibre-encrusting materials and the fibre being liberated in the next stage by the use of water only. As indicated, it appears that hydrogen ions liberated during this stage assist in freeing the cellulose fibre but in any event the relatively mild treatment avoids loss of and damage to to the fibre.

I claim:

1. A process for manufacturing sulphite pulp which comprises cooking cellulosic material with 1101.

sulphite liquor to sulphonate the lignin, discontinuing the cook before liberating the fibre, removing the liquor and further cooking the material with water to liberate the fibre.

3. In a two-stage process of manufacturing sulphite pulp, the steps which comprise discontinuing the first-stage cook before liberation of the fibre of the cellulose material and cooking with water to liberate the fibre.

4. A two-stage process of manufacturing sulphite pulp which comprises cooking cellulose ma terial with sulphite liquor until a temperature of 120 to 150 C. is reached, removing the liquor without substantially lowering the temperature or pressure, introducing preheated water and cooking the material to completely liberate the fibre.

5. A process as defined in claim 4, wherein said second-stage cook is effected at a temperature of 160 to 170 C. and a pressure of 85 to 100 pounds.

6. A process as defined in claim 4, wherein said first-stage liquor contains an excess of free sulphurous acid and wherein the second-stage cook is effected at a temperature of 160 to 170 C.

'7, A two-stage process of manufacturing sulphite pulp which comprises cooking wood chips with a sulphite liquor in which substantially 50% of the S02 is in the combined form, removing the liquor without substantially lowering the temperature or pressure, and cooking the chips with water at a temperature of 160 to 170 C. to liberate the fibre and hydrolyze the sulphonated lignin.

8. A process as defined in claim 7, wherein after the removal of the first stage liquor the material is washed with a preheated fluid to remove impurities.

' ERNST HOCHBERGER. 

